Corrosion is a significant problem in petroleum refineries and other industrial plants which process corrosive materials. Corrosion can cause deterioration of valves, gauges and other equipment. Corrosion can also cause leaks with large environmental and financial costs.
Corrosive species involved in the production and processing of crude oil and hydrocarbons may cause metal-loss corrosion of production, transfer, storage, and processing equipment. Erosive species typically involve fluid and/or solids turbulence causing metal loss from mechanical actions rather than chemical. For example, these corrosive/erosive species may be hydrocarbon, hydrocarbon containing materials, or aqueous, or combinations thereof. Moreover, streams may be single or multi-phase (solids, liquids, gases).
Various sensors can be used to monitor corrosion. In most cases, a sensor detects corrosion based on a correlation between a measurable property of a sensor, such as resonant frequency, and the corrosion rate. Typically a sensor will be connected to a display which can be monitored to determine the relative corrosion rate which has occurred on the sensor, and therefore potentially has occurred in an associated system. The most common areas of corrosion concern in a reaction system are at the interior wall of a pipe or vessel. In some cases, internal vessel components such as baffles or cyclones may also be subject to corrosion and/or erosion.
An important challenge in obtaining reliable corrosion estimates using a sensor disposed in a corrosive process fluid environment arises from the frequent changes in the physical properties of the fluid—such as temperature and viscosity—which alter the measured values for a sensor independent of corrosion. For example, for a sensor using a mechanical oscillator, changes in the resonant frequency that are unrelated to corrosion can be difficult to distinguish from the corrosion-related changes. This can lead to complications in attempting to determine a corrosion rate based on analysis of measured values related to a corrosion sensor. For a sensor using electrical resistance, changes in the element resistance that are unrelated to corrosion are similarly problematic.